Hours after Speaker Nancy Pelosi arrived in Taiwan, Beijing added economic measures to its series of retaliatory moves, suspending exports of natural sand to the island and stopping imports from Taiwan of certain types of fruit and fish. The bans are a vivid reminder for people in Taiwan that doing business with China, the island’s largest trading partner, can be risky during times of high geopolitical tension. China’s commerce ministry said on Wednesday that it had suspended natural sand exports to Taiwan, starting immediately. It gave no specific reason, saying in a brief statement only that it had done so…